The present invention generally relates to industrial automated material handling. More particularly, the present invention relates to an automated apparatus and method for releasing and handling a contact lens from a contact lens mold following formation of a contact lens therein. The invention is also applicable to other types of ophthalmic lenses, for example, spectacle and intraocular lenses.
Static cast molding of contact lenses is known. See, for example, U.S. Pat. No. 5,466,147 issued to Bausch and Lomb Incorporated, the entire reference of which is incorporated herein by reference. A single mold unit comprises a female mold section having a concave optical surface and a male mold section having a convex optical surface. The female and male mold sections are complimentary shaped and mateable to form a lens-molding cavity between the facing concave and convex optical surfaces of the female and male mold sections, respectively.
The basic process for cast molding a lens is as follows. A quantity of liquid lens material (monomer) is dispensed into the concave optical surface of the female mold section and the male mold section is seated upon the female mold section with the concave and convex surfaces thereof facing one another to form a lens-shaped mold cavity. The joined female and male mold sections form a single mold unit which is subject to a curing cycle (e.g., by thermal or UV radiation) thereby causing polymerization of the lens material in the mold cavity. Once the lens material has cured, the male and female mold sections must be separated to retrieve the cured lens.
The opening or release of the mold sections must be carried out in a manner which will not harm the delicate lens. Once the lens has polymerized in the mold cavity, the lens and any lens flash will have an adhesive bond to the opposite concave and convex mold surfaces. Thus, the release of the male mold section from the female mold section must be of a force strong enough to break the adhesive bond of the lens and lens flash to the opposing mold surfaces, yet not so strong or haphazard that the optical surfaces of the lens are harmed by the release process. Should the lens crack or be otherwise damaged during the mold release process, the lens must be scrapped, thereby lowering the output yield and increasing manufacturing costs.
An example of a mold release apparatus and method may be seen in PCT Published Application WO98/19854 which is assigned to Bausch and Lomb Incorporated, the present assignee herein and the entire disclosure of which is incorporated herein by reference. Another example of prior art methods of mechanical mold release include prying off of the male mold section from the female mold section by applying a lever-type mechanism between the two mold sections. See, for example, U.S. Pat. No. 5,693,268 issued to Johnson and Johnson Vision Products, Inc. which discloses an elongated wedge applied at opposite sides of the mold between the outer flanges of the male and female mold sections. The mold unit and wedge are translated relative to each other which gradually pries the male mold section from the female mold section.
Once the mold sections have been separated, the lens must be released from the mold section on which it is retained. Both wet and dry release methods of lens release have been proposed in the prior art. In wet lens release methods, an aqueous solution is used to wet the hydrophilic lens which thereby absorbs water and swells, causing the lens to separate from the mold surface. This method may also be used in the mold release procedure. In dry lens release methods, a force is applied to break the bond between the lens and mold surface. For example, the above-mentioned ""268 patent discloses that application of a thermal gradient between the male mold half and the lens contained therein may be used to assist in separating the lens from the mold. Other similar prior art methods are disclosed in the ""268 patent, and those references are hereby incorporated herein by reference.
Detaching a lens from a mold by deforming the mold body relative to the lens is seen in U.S. Pat. No. 4,909,969 issued to Wood. In this method, the mold body is compressed by using successively smaller diameter plungers which engage the interior of the mold resulting in a compressive force being applied to the mold wall. Permanent deformation of the mold body results with the lens ultimately detaching therefrom. A similar result can be accomplished by application of a pinching or squeezing force to the mold body. In the case of a male and female mold unit, the squeezing force is applied to one or both mold sections which deforms the mold, thereby assisting in release of the female from the male mold section.
Another factor to consider is how well the proposed mold release apparatus and method performs in a high speed automation environment, a very critical cost-to-manufacture consideration in today""s highly competitive contact lens industry. In many of the above prior art methods, the ability to consistently control the release operation degrades once applied to a high speed automated manufacturing line.
Yet another consideration is lens handling. Since contact lenses are extremely delicate, small articles of manufacture having precise optical surfaces, they must be handled with extreme care so as to not damage the lens and increase costs to the manufacturing operation. It is thus an object of a contact lens automation line to use a contact lens handling system which keeps the lenses from having to be directly touched by the handling machinery. In the case where the lenses must be transferred from the mold in which they were formed to a separate package for downstream processes (e.g., hydration) or for final packaging to the consumer (e.g., transfer to a blister package), the lenses must undergo some amount of handling to effectuate this transfer process. In prior art methods, lenses have been transferred manually by an operator using a pair of tweezers to grasp the lens and transfer it from the mold to a package receptacle. This, of course, is an extremely labor intensive method of lens handling and also creates a high chance of lens damage caused by the direct contact with the tweezers and the operator""s inability to consistently control the amount of force used with the tweezers when handling a lens therewith.
When transfer of the lens to a separate container is required as discussed above, it may be preferred to perform a dry lens release from the mold since the lens may be easier to handle in a manufacturing line when in a dry state as opposed to a wet state. This is since in the wet state of a soft contact lens, the lens is very flexible and prone to sticking and folding which could cause difficulties with the handling apparatus.
Once released from its associated mold surface, a dry lens is also prone to a problem known in the industry as xe2x80x9cfly-awayxe2x80x9d. This is the phenomenon of a dry lens being displaced from its intended location due to air currents and/or electric charges surrounding the manufacturing line. Such air currents can develop by the moving parts of the machinery and/or workers moving about the automation line, for example. Further, static electricity is typically generated by the automation equipment in the manufacturing line. The lens fly-away problem creates an increase of xe2x80x9cno lensxe2x80x9d situations in the receptacle in which the lens was intended to be placed, thus increasing down time and manufacturing costs to detect and correct xe2x80x9cno lensxe2x80x9d occurrences.
There thus remains a need for an apparatus and method for dry releasing a contact lens from its associated mold section and which substantially eliminates fly-away lenses during handling, and which is capable of robust, consistent performance in a high speed, automated manufacturing environment.
The present invention addresses the problems of prior art dry lens release methods and apparatus by providing in a first aspect an apparatus and method for dry releasing a contact lens from its associated mold section in a manner which is non-destructive to the lens, and which is capable of high speed automation in a manufacturing line. In a second aspect, the invention provides an apparatus and method for transferring a dry contact lens from its associated mold section to a separate receptacle which is not only non-destructive to the lens, but also prevents the phenomenon of unintentional lens displacement (hereinafter xe2x80x9cfly-awayxe2x80x9d).
More particularly, the present invention comprises an in-line manufacturing cell which is operable to accept an array of individual contact lens mold sections each containing a cured lens therein, release the lens from its associated mold section, and lift and transfer the lens to a separate receptacle in a manner which positively captures the lens in the receptacle, thereby substantially eliminating the chance of lens fly-away.
Thus, prior to entering the lens release and transfer cell, the mold units have been subjected to a curing process to cure the lens material, and the female and male mold units have been separated to reveal the lens which is retained on one of the mold surfaces. In the preferred embodiment of the invention, the lens is retained in the female (concave optical molding surface) mold section. Preferentially retaining a lens in a desired mold section is known in the art, and may be accomplished by a variety of methods, including, for example, the mold configuration and geometry of the respective surfaces; electrochemical or other surface treatments to one of the mold surfaces; and/or using different materials to make the male and female mold sections, thereby causing one mold section to have a greater affinity to the lens material as compared to the other mold section.
A predetermined number of mold sections with lenses retained therein are positioned on a mold pallet or other suitable support which positions the mold units in a predetermined array on the pallet. The pallet is advanced into the lens release and transfer cell which transports the pallet with mold sections thereon to a lens release station within the cell. At the lens release station, a pin is operable to rise from beneath a respective mold section and engage the surface of the mold section opposite the optical surface containing the lens. A predetermined force is applied to the mold section by the pin which thereby acts to slightly deform the mold surface which breaks the adhesive force between the optical molding surface and the lens.
Prior to the pin releasing the lens from the mold section, a vacuum head is lowered over the pallet which has previously picked up a pallet cover which is releasably coupled to the vacuum head unit. As soon as the lens is released from the mold surface by the pin acting from beneath the pallet, the vacuum head is activated to pick the lens up and out of the mold section. The vacuum head transports the lens together with the pallet cover to a second pallet which holds a receptacle for each lens. In the preferred embodiment, the receptacle is a blister package having a concave well into which the lens is placed for hydration and final packaging.
With the vacuum head aligned over a respective receptacle, the vacuum is released and the lens is deposited into the receptacle of the second pallet. The vacuum head is then raised, leaving the pallet cover on top of the second pallet. The hole in the pallet cover through which the vacuum head extends is of a diameter large enough to permit insertion and withdrawal of the vacuum head, yet small enough to prevent passage of the lens therethrough. In this way, the pallet cover operates to confine the lens within its respective receptacle, thereby preventing the problem of lens fly-away.